Adjustable resistance



F. E. HESSEY 2,368,710

ADJUSTABLE RES I STANCE Feb. 6, 1945.

Filed Sept. 19, 1942 I6 INVENTOR.

FREDERIC E. HESSEY.

ATTORNEY.

Patented Feb. 6,; 1945 ADJUSTABLE RESISTANCE Frederic E. Hessey, Manoa,Pa., assignor to The Brown Instrument Company, Philadelphia, Pa., acorporation of Pennsylvania P Application September 19, 1942, Serial No.458,985

v 12 Claims. This invention relates to adjustable resistances in generaland more particularly to adjustable potentiometer resistances such asdisclosed in T. R. Harrison et a1. Patent No. 2,150,502, granted March14, 1939, or in W. P. Wills application Ser. No. 421,173, filed December1, 1941.

Adjustable potentiometer resistances are utilized in potentiometermeasuring instruments for accurately measuring small electromotiveforces and successful operation of such potentiometer measuringinstruments is directly dependent upon the construction and accurateoperation of the adjustable potentiometer resistances. Small changes incontact resistance or wear due to prolonged use ma produce greatereffects than the small electromotive forces being measured and it isdesirable to maintain these effects at a minimum.

Accordingly, the prime object of this invention is to provide animproved adjustable resistance, and more particularly an improvedadjustable potentiometer resistance, wherein changes in contactresistance and the effects due to wear are reduced to a minimum,accuracy and uniformity of operation is enhanced and wherein the cost ofmanufacture is materially reduced.

In accordance with.- this invention the improved adjustable resistancemay comprise an elongated resistance element and collector, a contactcarrier movable lengthwise with respect to the resistance element andcollector but-at an angle with-respect thereto and including a slotsubstantially transverse with respect to the direction of movement, anda contact having sloping ends carried between the contact carrier memberand the resistance element and collector with the contact slidablyengaging the resistance element and collector and the sloping endsrotatable engaging the edges of the/slot. As the contact carrier memberis moved,a new contacting surface of the contact i continuously anduniformly presented to the resistance element thereby decreasing thecontact resistance, and affording accurate and uniform operation. Thecontact may take the form of a sphere, a cylinder with conical ends, abarrel with conical ends or anyother' similar shape. The contact may bemade of softer material than the resistance element so that wear takesplace on the readily replaceable contact and not on the resistanceelement and collector. The contact my be provided with a handle tofacili te insertion of the contact between the contact carrier memberand the resistance element and collector. The contact may be made ofsofter material than of the invention.

the contact carrier member whereby the edges of the slot automaticallyform an axle on the sloping surfaces of the contact for free rollingcontact therewith. This obviates the necessity of accurately machiningthe contact to obtain the desired fit with respect to the slot andthereby greatly decreases the cost of manufacture thereof. To providethese aforementioned improved features also form. specific objects ofthis invention.

The various features of novelty which characterize this invention arepointed out with particularity in the claims annexed to and forming apart of this specification. For a better understanding of the invention,however, its ad-- vantages and specific objects obtained with its use,reference should be had to theaccompanying drawing and descriptivematter in which is preferred embodiment illust ated and described aFigs. 5 and 6 are views similar to Figs. 2 and 4, respectively, of a.modified form of apparatus;

and

comprises a cylindrical base ll formed of in-.

sulating material, such as ceramic, and suitably secured to a bracket I2which is utilized for mounting purposes. The cylindrical base II isprovided with helical grooves l3 and I4, the grooves being uniformly andclosely spaced with respect to each other and extending in a helixaround the cylindrical base II. A collector II and a resistance elementI6 are mounted in the grooves l3 and M, respectively. The collector l5may be formed by helically winding a wire about another wire, the twowires forming the collector I5 preferably being in electrical contactthroughout the length of the collector. The rewound about an insulatedwire. Preferably the collector II and the resistance element It are ofthe same diameter and are formed of the same material, such as manganin.The bracket l2 may carry a terminal block I! provided with terminals II,I! and 20 to which are electrically connected the collector i and theresistance element II.

An arm II is adjustably secured to one end of a shaft 26 which extendscoaxially through the cylindrical base II and is provided with a drivingmeans, such as a cable operated drum 2! at the other end. Rotation ofthe drum 21 causes rotation of the shaft 28 and rotation of the arm 25about the cylindrical base H. A contact-carrier member in the form of aspring arm 28 is secured to the arm 25 by means of rivets II and issuitably insulated from the arm 25 by insulating pads 29. The contactcarrier member or spring arm 28 is preferably made of hardened berylliumcopper and is provided with a slot 38 which is substantially transversewith respect to the direction of movement of the spring arm 20. Acontact 38, which is made of a softer material than the collector l5,resistance element It and spring arm 28, is interposed between thespring arm 28 and the collector and resistance element and is held inplace by the resilient force of the spring arm 28. The contact 38operates in the slot 38 in a manner to be pointed out more fullyhereafter. The contact 36 may be made of sterling silver or likematerial. Since the collector l5 and resistance element ii are helicallywound on the cylindrical base ii, the spring arm 28 moves along thelength of the collector and resistance element but also moves at anangle with respect thereto so that as the contact I! is moved around thecylindrical base II it must necessarily move upwardly and downwardly inthe slot 35.

Figures 2 and 3 illustrate more clearly the construction and mode ofoperation of contact 3! with respect to the collector i5, resistanceelement II and the slot I5 in the spring arm 28. The contact 38 rotatesabout an axis as it is bodily moved and the contact is provided at theends of the axis with sloping surfaces, which may be substantiallyconical surfaces 31 shown in Fig. 2. The periphery of the contact 88engages the c0llector I! and resistance element It for-longitudi nal androtational sliding movement with respect thereto and the conicalsurfaces 31 engage the edges of the slot 35 for rolling movement withrespect thereto.

When the spring arm 28 moves to the left as shown by the arrow A in Fig.2 it moves upwardly away from the plane of the drawing in Fig. 3 asdesignated at 8.. Such movement causes movement of the contact N to theleft in Fig. 3 as illustrated by the arrow C since the helical windingof the collector II and resistance element It extends in that generaldirection, as illustrated. As a result of such movement and due to theforces present and the friction effects where the edges of the slot 35engage the conical surfaces provides a wiping action which maintainscontact resistance at a minimum.- When the adjustable resistanceassembly is first operated there is an appreciable wedging actionbetween the edges of the slot 35 and the conical surfaces 11 whichproduces a large force at these points of contact. This force insuresrolling of the conical surfaces 31 along the edgesof the slot 35 andalso causes the edges of the slot to form slight grooves or tracks inthe conical surfaces 31 as illustrated at 39 in Fig. 3. These grooves ortracks 39, being formed during actual operation of the contact 38.

with respect to the slot Q5, form an accurate and true surface forrolling. contact between the contact 36 and the edges of the slot 35.Too close a fit which would cause binding or too wide a fit which wouldcause lost motion and cooking of the contact are thereby automaticallyeliminated. It is found that after a long period of operation thisgroove or track enlarges to form a pronounced axle as illustrated at M)in Fig. 4 which axle continues to guide rotatably and freely the contact36 in the slot 35.

' This type of contact, which wears itself in to fit the slot 35, doesnot require hand fittingin order to eliminate lost motion or binding. Itis not necessary to finish the wearing surfaces of the contact 35 otherthan roughly forming the such a contact. Since the contact 35 is ofsofter material than the collector 15' and the resistance element It,any wear that takes place takes place on the contact 38 and not on thecollector I5 and resistance element l6, and since the con tact 36 iscontinuously rotated by its rolling contact with the edges of the slot35, a new contacting surface is always presented to the collector i5 andresistance element i6 whereby the wear on the contact 36 is evenlydistributed about the periphery thereof. Since the contact (it is ofsofter material than the spring arm any wear due to rolling actionbetween the c 38 and the edges of the slot 35 is taken the contact 3!which is readily replaceable. litter the contact has performed itsoperation over a long period of time it may be readily r ced by a newcontact for another long period of serviceable opera tion. In order tofacilitate insertion of the contact in the slot 35 the contact may beprovided with a handle 38 to provide a place to grip the contact with apair of tweezers or long nose Figures 2, 3 and 4. The arrangementof Fig-I1 and where the periphery of the contact 38 engages the collector Iiandresistance I 8, the .contact rolls along the edges of slot androtates in a clockwise direction in Fig. 3 as indicated by the arrow D.This clockwise rotation and rolling of the contact 38 as it'is moving tothe left continuously presents a new contact surface to the collector IIand resistance element II as it is moved bodily therealong and it alsois ure 7 operates in identically the same manner as the arrangement ofFigures 2, 3, and 4 and, therefore, a further description of thisarrangement is not considered necessary.

While the contacts 38; 38' and 38" have generally differentconfigurations, they all are, circular in cross section about their axesof rotation for contacting the collector I! and resistance element Itand have sloping surfaces at the ends of the axes for rolling engagementwith the edges of the slot 35. While the collector l5 andresist anceelement It areshowninl 'ig. 1 tobehelically wound .about a cylindricalbase H, they may be spirally wound on a flat base or longitudinallylocated on an elongated flat base and the same mode of operation isaccomplished. In each of these instances, the contact carrier member 28while moving longitudinally of the collector l and resistance It alsomoves at an angle with respect thereto so that the contact 36 will rollin the slot 35.

While in .accordance with the provisions of the statutes, I haveillustrated and described the best form of this invention now known tome, it will be apparent to those skilled in the art that changes may bemade in the form of the apparatus disclosed without departing from thespirit of this invention as set forth in the appended claims, and thatin some cases certain features of this invention may sometimes be usedto advantage without a corresponding use of other features.

Having .now described this invention, what I claim as new and desire tosecure by Letters Patent is:

- 1. In an adjustable resistance, the combination of, a resistanceincluding a plurality of elongated resistance elements uniformly andclosely spaced with respect to each other, a contact carrier wise withrespect to the elongated elements but at an angle with respect theretoand including ber movable lengthwise with respect to the elongatedelements but at an angle with respect thereto and including a slotsubstantially transverse with respect to the direction of movement, anda spherical contact carried between the contact carrier member and thepair of elongated resistance'eleinents with a portion thereof engagingeach of the elongated resistance elements for sliding contact therewithand with portions thereof engaging. the edges of the slot for rollingcontact I therewith.

member movable lengthwise with respect tothe elongated elements but atan angle with respect thereto and including a slot substantiallytransverse with respect to the direction of movement,

and a contact, circular in cross section about an axis and sloping atthe ends of the axis, carried between the contact carrier member and thepair of elongated resistance elements with the circumference thereofengaging each of. the elongated resistance elements for sliding contacttherewith and with the sloping surfaces thereof engaging the edges ofthe slot for rolling contact therewith.

2. In an adjustable resistance, the combination of, a resistanceincluding elongated elements uniformly and closely spaced with respectto each other, a contact carrier member movable length- 6.. In anadjustable resistance, the combination of, a resistance includingelongated elements uni;- formly and closely spaced with respect to eachother, a contact carrier member movable lengthwise with respect to theelongated elements but at an angle with respect thereto and including aslot substantially transverse with respect to the direction of movement,and a contact, circular in cross section about an axis and sloping atthe ends of the axis, carried between the contact car-' rier member andthe elongated elements with wise with respect to the elongated elementsbut at an angle with respect thereto and including a slot substantiallytransverse with respect to the direction of movement, and a contact,circular in cross section about an axis and substantiallyv conical atthe ends of the axis, carried between the contact carrier member and theelongated elements with the circumference thereof engaging the elongatedelements for sliding contact therewith and with the substantiallyconical surfaces thereof engaging the edges of the slot for rollingcontact therewith.

3. In an adjustable resistance, the combination of, a resistanceincluding. elongated elements uniformly and closely spaced with respectto each other, a contact carrier member movable lengthwise with. respectto the elongated elements and collector but at an angle with respectthereto and including a slot substantially transverse with respect tothe direction of movement, and a substantially cylindrical contact withsubstantially conical ends carried between the contact carrier memberand the elongated elements with the substantially cylindrical surfacethereof engaging V the elongated elements for sliding contact therewithand with the substantially conical ends thereof engaging the edges ofthe slot for rolling contact therewith. v

4. In an adjustable resistance, the combination of, a'resistanceincluding elongated elements uniformly and closely spaced with respectto each other, a contact carrier member movable lengththe circumferencethereof engaging the elongated elements for sliding contact therewithand with the sloping surfaces thereof engaging the edges of the slot forrolling contact therewith, said contact being formed of softer materialthan the elongated elements whereby wear due to sliding contact is takenby the contact.

7. In an adjustable resistance, the combination of, a resistanceincluding elements uniformly and closely spaced with respect to eachother, a contact carrier member-movable lengthwise with respect to theelongated elements but at an angle with respect thereto and including aslot substantially transverse with respect to the direction of movement,and a contact, circular in cross section about an axis and sloping at"the ends of the axis, carried between the contact carrier member andthe elongated elements with the circumference thereof engaging theelongated elements for sliding contact therewith and with the slopingsurfaces thereof engaging the edges of the slot for rolling contacttherewith, said contact being formed of softer material than the contactcarrier member whereby the edges of the slot form an axle on the slopingsurfaces of the contact for rolling contact therewith.

8. In an adjustable resistance, the combination of, a resistanceincluding elongated elements uniformly and closely spaced with respectto each other, a contact carrier member movable lengthends of the axis,carried between the contact carrier member and the elongated elementswith the circumference thereof engaging the elongated elements forsliding contact therewith and with the sloping surfaces thereof engagingthe edges of the slot for rolling contact therewith, and a handle formedon said contact to facilitate insertion of the contact between thecontact carrier member and the elongated elements. 9. In an adjustableresistance, the combina-' tion of, a resistance including elongatedelements uniformly and closely spaced with respect to each other, acontact carrier member movable lengthwise with respect to the elongatedelements but at an angle with respect thereto and including a slotsubstantially transverse with respect to the direction-of movement, acontact, circular in cross section about an axis and sloping at the endsof the axis, carried between the contact carrier member and theelongated elements with the circumference thereof engaging the elongatedelements for sliding contact therewith and with the sloping surfacesthereof engaging the edges of the slot for rolling contact therewith,said contact being formed of softer'material the elongated elementswhereby wear due v to sliding contact is taken by the contact, and ahandle formed on said contact to facilitate insertion of the contactbetween the contact carrier member and the elongated elements.

10. In an adjustable resistance, the combination of, a resistanceincluding elongated elements uniformly and closely spaced with respectto each other, a contact carrier member movable lengthwise with respectto the elongated elements but at an angle with respect thereto andincluding a slot substantially transverse with respect to the directionof movement, and a contact, circular in cross section about an axis andsloping at the ends of the axis, carried between the contact carriermember and the elongated elements with the circumference thereofengaging the elongated elements for sliding contact therewith andwiththe sloping surfaces thereof engaging the edges of the slot for rollingcontact therewith, said contact being formed of softer material than theelongated elements whereby wear due to sliding contact is taken by thecontact, and said contact being formed of softer material than thecontact carrier member whereby the edges of the slot form an axle on thesloping surfaces of the contact for rolling contact therewith.

11. In an adjustable resistance, the combination of, a resistanceincluding elongated elements uniformly and closely spaced with respectto each other, a contact carrier member movable lengthwise with respectto the elongated elements but at an angle with respect thereto andincluding a slot substantially transverse with respect to the directionof movement, a contact, circular in cross section about an axis andsloping at the ends of the axis, carried between the contact carriermember and the elongated elements with the circumference thereofengaging the elongated elementsfor sliding contact therewith and withthe sloping surfaces thereof engaging the edges of the slot for,rollin'gcontact therewith, said contact being formed of softer material than,the contact carrier member whereby the edges of the slot form an axle onthe sloping surfaces of the contact for rolling contact therewith, and ahandle formed on said contact to facilitate'insertion of the contactbetween the contact carrier member and the elongated ele-- ments.

12. In an adjustable resistance, the combination of, a resistanceincluding elongated elements uniformly and closely spaced with respectto each other, a contact carrier member movable lengthwise with respectto the elongated elements but at an angle with respect thereto andincluding a slot substantially transverse with respect to the directionof movement, a contact, circular in cross section about an axis andsloping at the ends of the axis, carried between the contact carriermember and the elongated elements with the circumference thereofengaging the elongated elements for sliding contact therewith I and withthe sloping surfaces thereof engaging the edges of the slot for rollingcontact therewith, said contact being formed of softer material than theelongated elements whereby wear due to sliding contact is taken by thecontact, said contact being formed of softer material than the contactcarrier member whereby the edges of the slot form an-axle on the slopingsurfaces of the contact for rolling contact therewith, and a handleformed on said contact to facilitate insertion of the contact betweenthe contact carrier member and the elongated elements.

FREDERIC E. HESSE'Y.

